1) Field of the Invention
This invention relates to a webbing retractor suitable for use in a vehicle seat belt system, especially to a webbing retractor in which a pawl pin supporting portion of a side wall of the retractor base is prevented from being deformed by loads applied to a pawl pin.
2) Description of the Prior Art
FIG. 1 shows the structure of a typical webbing retractor in order to facilitate the understanding of the present invention. There are shown a base 1 of the webbing retractor, side walls 2,3 of the base 1, a spool 4 with a webbing wound thereon, a released portion 4' of the webbing, a take-up spindle 6 supported rotatably on the base 1 and holding the webbing at the inner end thereof, a ratchet wheel 5 mounted on the take-up spindle 6 so as to allow the ratchet wheel 5 to rotate together with the take-up spindle 6, a pawl 7, a pawl pin 8, a pendulum-like control member 9, and a cover 10 enclosing a take-up spring (not shown) for the webbing.
FIG. 2 illustrates the operation of the pawl 7. The pawl 7 is in engagement with the ratchet wheel provided on the base 1. The pawl 7 is attached on the side wall 2 by way of the pawl pin 8.
FIG. 3 shows the manner of attachment of the pawl pin 8. The pawl pin 8 is force-fit at a small-diameter portion 81 in the side wall 2, so that the pawl pin 8 is supported in a cantilevered state. When the pendulum-like control member 9 is swung in the event of an emergency of the vehicle, the pawl 7 is upwardly brought into engagement with the ratchet wheel and a force is hence applied to the pawl 7 as depicted in FIG. 4, and as a result, a load is exerted on the pin 8 as indicated by P in FIG. 3. As shown in FIG. 5, the pin supporting portion of the side wall 2 is thus deformed as indicated by numeral 21. In FIG. 4, R indicates the direction of rotation of the ratchet wheel 5. When a load is applied to the pin 8 and the side wall 2 is deformed as a result, the center of the pin 8 is shifted in the direction indicated by the arrow D so that the distance between the center of the take-up spindle 6 and that of the pin increases. As a result, the pawl 7 is caused to turn as indicated by the arrow a. The retractor is therefore unstable and is susceptible to damages even by small loads. The pin 8 is easily slipped off when the pin 8 is supported in a cantilevered state as shown in FIG. 3. It may be therefore be contemplated to provide a large-diameter portion 82 with the pin 8 inside the side wall 2 as depicted in FIG. 6. However, the pin supporting portion of the side wall 2 is still prone to deformation as indicated by numeral 21 by the load P applied to the pin 8 as illustrated in FIG. 7.
In order to prevent the pawl pin 8 from being easily slipped off by bending moments, it has also been proposed to support the pin 8 between the side walls 2 and 3 as shown in FIG. 8 or to provide a reinforcement plate 11 between the take-up spindle 6 and pawl pin 8 as depicted in FIG. 9. Although the pawl pin 8 is not supported in a cantilevered state but is supported at both ends thereof, it is still impossible to avoid the deformation of the side walls or reinforcement plate when loads are applied to the pawl pin 8.
It may be contemplated to increase the wall thickness of the base at the pin supporting portion or portions only. This approach however results in cumbersome fabrication, leading to an inevitable increase to the manufacturing cost.